1. Field of the Invention
The present invention relate s to a high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance. In particular, the present invention relates to a high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance which is used as a constituent material for a working fluid passage of a heat exchanger joined by brazing, such as an evaporator for an automotive air conditioner or a radiator, and has particularly excellent corrosion resistance and excellent formability before brazing, and high strength after brazing.
2. Description of Background Art
Heat exchangers made of an aluminum alloy have been widely used as radiators, oil coolers, inter-coolers, heaters, and evaporators for air conditioners for automobiles, and condensers and oil coolers for hydraulic devices or industrial machines. Various types of heat exchangers made of an aluminum alloy are known. Among these, a laminated heat exchanger (drawn-cup type heat exchanger) has attracted attention because of its light weight. Such a drawn-cup type heat exchanger is fabricated by forming working fluid passages by laminating formed aluminum alloy clad materials, combining corrugated fins made of an aluminum alloy between the working fluid passages, and integrally brazing these materials.
As shown in FIGS. 1 and 2, a drawn-cup type evaporator has press-formed core plates 11 and 12 made of aluminum alloy clad materials and a corrugated fin 13 made of an aluminum alloy laminated thereon. The core plates 11 and 12 and the fin 13 are brazed by melting a brazing material in the core plates 11 and 12, thereby forming a passage 14 for a working fluid such as a refrigerant between the core plates 11 and 12.
As the core plates 11 and 12, aluminum alloy clad materials having a core material and a brazing material are used. The core material is formed of an aluminum alloy containing Mn such as an Alxe2x80x94Mn alloy, Alxe2x80x94Mnxe2x80x94Cu alloy, Alxe2x80x94Mnxe2x80x94Mg alloy, or Alxe2x80x94Mnxe2x80x94Cuxe2x80x94Mg alloy (JIS A3003 alloy, JIS A3005 alloy, etc.). The brazing material is formed of an Alxe2x80x94Si alloy such as an Alxe2x80x94Si alloy, Alxe2x80x94Sixe2x80x94Mg alloy, Alxe2x80x94Sixe2x80x94Mgxe2x80x94Bi alloy, Alxe2x80x94Sixe2x80x94Mgxe2x80x94Be alloy, Alxe2x80x94Sixe2x80x94Bi alloy, Alxe2x80x94Sixe2x80x94Be alloy, or Alxe2x80x94Sixe2x80x94Bixe2x80x94Be alloy. Either one or both sides of the core material is clad with the brazing material.
An aluminum alloy containing an Alxe2x80x94Mn alloy to which Cu, Mg, Zn, Sn, In, and the like are added is used as the fin 13. The fin 13 and the core plates 11 and 12 are usually brazed by vacuum brazing. Moreover, flux brazing using chloride flux or fluoride flux is also used.
In recent years, reduction of the weight and manufacturing cost of heat exchangers has been strongly demanded. To deal with this demand, it is necessary to further decrease the thickness of the constituent materials of heat exchangers, such as those for a working fluid passage. However, when the strength of aluminum alloy clad materials used to form a working fluid passage is increased in order to decrease the thickness, formability is impaired due to the decreased amount of elongation. Moreover, corrosion resistance decreases, thereby causing the fabricability and durability of the heat exchangers to decrease. Therefore, development of clad materials exhibiting improved elongation (formability), strength after brazing, and corrosion resistance has been demanded.
Aluminum alloy clad materials used as the core plates 11 and 12 of the drawn-cup type evaporator 10 have a core material made of an aluminum alloy containing Mn. Therefore, these materials exhibit inferior pitting-corrosion resistance. For example, when applied to a working fluid passage for a refrigerant, perforation leakage may occur due to pitting.
Pitting-corrosion resistance of working fluid passage materials may be improved by using materials for which the potential is lower than that of the working fluid passage materials, such as an Alxe2x80x94Mxe2x80x94Zn alloy, Alxe2x80x94Mxe2x80x94Sn alloy, or Alxe2x80x94Mxe2x80x94In alloy as the fin 13. The sacrificial anode effect of the fin 13 made of these materials provides the working fluid passage materials with corrosion resistance. However, occurrence of pitting-corrosion in the working fluid passage material can be prevented only in the area near the fin 13. Occurrence of pitting-corrosion in the working fluid passage material is inevitable in the area apart from the fin 13 because the sacrificial anode effect of the fin 13 is not obtained.
The following materials are proposed as aluminum alloy clad materials for working fluid passages exhibiting improved corrosion resistance: (1) a clad material in which Cu, Ti, Cr, or Zr is added to the core material thereof (Japanese Patent Publication 41621/1994, Japanese Patent Application Laid-open No. 241133/1988, Japanese Patent Application Laid-open No. 83396/1989, and Japanese Patent Application Laid-open No. 258945/1990); (2) a clad material in which the content of Fe, which forms a compound functioning as a cathode and decreases corrosion resistance in the core material, is limited to 0.2% or less (Japanese Patent Application Laid-open No.83396/1989); and (3) a clad material exhibiting improved intergranular corrosion resistance in which the Fe content and the Si content in the core material are limited (Japanese Patent Publication 41621/1994 and Japanese Patent Application Laid-open No. 241133/1988). Although these aluminum alloy clad materials exhibit improved corrosion resistance, these materials cannot fully satisfy the demand for improved formability and strength after brazing.
In order to obtain an aluminum alloy clad material which can solve the above problems in conventional working fluid passage materials and satisfy the demand for reduced thickness, the present inventors have conducted extensive experiments and studies on the composition of the core material, the composition of the brazing material used to clad both sides of the core material, and the effects of the combination of these materials on formability, strength after brazing, brazability, and corrosion resistance. Accordingly, an object of the present invention is to provide a high-strength aluminum alloy clad material for heat exchangers which has excellent corrosion resistance and superior formability before brazing, is easily brazed, and has improved strength after brazing.
In order to achieve the above object, the present invention provides the following high-strength aluminum alloy clad materials for heat exchangers exhibiting excellent corrosion resistance.
(1) A high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance comprising a core material and a brazing material, with either one or both sides of the core material clad with the brazing material, wherein the core material comprises an aluminum alloy comprising from 0.3% to less than 0.6% of Mn, from more than 0.6% to 1.0% of Cu, less than 0.1% of Si, 0.3% or less of Fe, and from 0.06% to 0.35% of Ti, with the remainder consisting of Al and impurities; and the brazing material used to clad either one or both sides of the core material comprises an Alxe2x80x94Si aluminum alloy in which the Ca content is limited to 0.006% or less.
(2) A high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance comprising a core material and a brazing material, with either one or both sides of the core material clad with the brazing material, wherein the core material comprises an aluminum alloy comprising from 0.3% to less than 0.6% of Mn, from more than 0.7% to 1.0% of Cu, less than 0.1% of Si, 0.3% or less of Fe, and from 0.06% to 0.35% of Ti, with the remainder consisting of Al and impurities; and the brazing material used to clad either one or both sides of the core material comprises an Alxe2x80x94Si aluminum alloy in which the Ca content is limited to 0.006% or less.
(3) A high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance comprising a core material and a brazing material, with either one or both sides of the core material clad with the brazing material, wherein the core material comprises an aluminum alloy comprising from 0.3% to less than 0.6% of Mn, from more than 0.6% to 1.0% of Cu, less than 0.1% of Si, 0.3% or less of Fe, from 0.06% to 0.35% of Ti, and from 0.06% to 0.7% of Mg, with the remainder consisting of Al and impurities; and the brazing material used to clad either one or both sides of the core material comprises an Alxe2x80x94Si aluminum alloy in which the Ca content is limited to 0.006% or less.
(4) The high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance according to the above (3), wherein the Cu content in the core material is from more than 0.7% to 1.0% or less.
(5) The high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance according to the above (3), wherein the Mg content in the core material is from 0.06% to 0.5%. (6) The high-strength aluminum alloy clad material for heat exchangers exhibiting excellent corrosion resistance according to the above (4), wherein the Mg content in the core material is from 0.06% to 0.5%.